1. Field of the Invention
The present invention relates to an apparatus and a method for guaranteeing the minimum cell rate of each connection accommodated in a communication network.
2. Description of the Related Art
These days, along with the development of information apparatuses, a variety of items of information have been exchanged between these apparatuses through a communication network. In a conventional communication network, as represented by a telephone system, the main target of communication is speech, and the required transmission rate of information is not so high. However, when so-called multimedia information, such as speech, pictures, data, etc. are exchanged using an information apparatus, transmission capability required by a communication network varies depending on the characteristic of each information. When the multimedia information, such as speech, pictures, data, etc. are exchanged at high speed, the transmission rate of a communication network has to be very high. Taking such demands into consideration, a broadband ISDN (B-ISDN) system has a bright future ahead as a communication system for integrating and accommodating a variety of media information, such as speech, pictures, data, etc. In particular, an asynchronous transfer mode (ATM) is a central transmission technology of the broadband ISDN, and the research and development of ATM communication apparatuses, such as an ATM exchange employing this technology, etc. are actively made by every telecommunications manufacturer.
Currently, the standardization of a guaranteed frame rate (GFR) is promoted as a new service class for efficiently accommodating high-burst communications into an ATM network, in the Telecommunication Committee of International Telecommunication Union (ITU-T), ATM-Forum, etc. The GFR guarantees a user the throughput of data at a rate up to a minimum cell rate (MCR) reported by the user, and when a line is empty, the user can also transfer data at a rate exceeding the MCR. One of the features of the GFR is that network resources can be efficiently utilized by sharing a rate band with a plurality of connections and simultaneously the minimum service described above can be guaranteed.
There are roughly the following two methods of controlling a cell input rate needed to implement this.
(1) A first-in first-out (FIFO) buffer for accommodating cells with a plurality of connections is adopted, and if the volume of cells staying unprocessed exceeds a certain threshold, cells other than those with up to an MCR are not inputted to the FIFO in each connection.
(2) A buffer for storing cells is provided individually for each connection, and the cells are read from the individual buffer at intervals of at least 1/MCR.
In a FIFO type GFR as described in the above (1), input traffic is measured for each connection, tagging is performed for cells with a connection made at the rate exceeding an MCR, and the FIFO discards on input, cells meeting the following two conditions.
Cells, if the amount of buffered cells exceeds a certain threshold
Cells which are tagged
FIG. 1 shows the configuration of an apparatus providing a conventional FIFO type GFR.
In the conventional FIFO type GFR, using both congestion monitoring information b from a queue length monitor unit 273 for monitoring whether or not the volume of cells queued in the FIFO 272 exceeds the threshold, and rate-over information a (information indicating whether or not an incoming cell has been transmitted at a rate exceeding the MCR) from a rate measurement unit 271, an input control unit 274 controls the input of cells into a FIFO 272 by turning on/off a switch 276. The rate measurement unit 271 measures the number of cells corresponding to the MCR of each connection (number of MCR cells) set for each connection, and judges whether or not the input cell rate of each connection exceeds the MCR while searching and referring to an MCR storage unit 275 (usually composed of memories).
The rate measurement unit 271, for example, comprises for each connection a counter 282 for counting down, with cells of a number corresponding to the MCR as shown in FIG. 2 as an initial value every time a cell is input. The rate measurement unit 271 also comprises a connection identification unit 281 for identifying a connection based on an identifier set in the header of the cell, such as a virtual path identifier (VPI), a virtual channel identifier (VCI), etc. The rate measurement unit 271 outputs the rateover information a with an incoming cell, after the count value of the counter 282 becomes xe2x80x9c0xe2x80x9d as a cell with a rate exceeding the MCR of a connection which has transmitted the incoming cell. The counter value of the counter 282 is reset at a predetermined constant time, and a number of cells corresponding to the MCR of a corresponding connection is set in the counter 282 again as an initial value.
The queue length monitor unit 273 compares the queue length of the FIFO 272 with a predetermined threshold, and judges whether or not the number of cells stored in the FIFO 272 exceeds the threshold, that is, for example, if the. FIFO 272 is about to overflow. The queue length monitor unit 273 can be easily composed using comparators.
According to the configuration described above, if a rate is less than the MCR, all the cells of each connection are inputted to the FIFO 272, and share among the connections xe2x80x9ca rate band exceeding the sum of the MCR of each connectionxe2x80x9d (hereinafter called xe2x80x9cavailable rate bandxe2x80x9d) out of the allowable rate bands of the FIFO 272.
Therefore, if there is no available rate band, a rate band up to the MCR reported by each connection can be used, and as a result, fairness is improved. Generally speaking, the sum of the MCRs of each connection becomes less than the read rate of the FIFO 272 (in order to guarantee the MCR of each connection). Therefore, when there is a connection not communicating, the MCR becomes an available rate band for other connections.
An MCR can be guaranteed by either of the above methods (1) and (2). However, when a FIFO is used, a buffer is shared with a plurality of connections, and the part of a rate band exceeding the MCR is occupied by each connection in proportion to the input rate of the FIFO, which is a problem from the viewpoint of impartiality among users. That is, how to distribute an available rate band among the connections is not predetermined, and the part exceeding the MCR of cells inputted to the FIFO are left to be occupied by arbitrary incoming cells. Therefore, there is a possibility that a connection transmitting the largest volume of cells to the FIFO at a certain time may occupy the FIFO. That means that, even a connection with a low MCR value often can use the FIFO more frequently than a connection with a high MCR value, that is, even a connection with a low MCR value can transmit cells at a higher rate, which causes an unfair.
However, since a FIFO can be configured more easily and a necessary buffer capacity can be made less than an individual buffer by the effect of sharing, the FIFO is useful as means for implementing a GFR, only if fairness among users can be implemented.
It is an object of the present invention to provide an apparatus and a method for making more efficient use of network resources possible in a network by fairness distributing an available rate band between the connections while guaranteeing an MCR for each connection.
The rate band managing apparatus of the present invention for guaranteeing the MCR of each of connections accommodated in a network, comprises a re-calculator unit for re-calculating an MCR value to be guaranteed for each of the connections according to a predetermined rule and obtaining the virtual MCR (re-calculated MCR) of each of the connections, and a control unit for guaranteeing the MCR of each of the connections using the virtual MCR of each of the connections.
The rate band managing method of the present invention is a rate band managing method for guaranteeing the MCR of each of connections accommodated in a network, and comprises the steps of (a) re-calculating the MCR value to be guaranteed for each of connections according to a predetermined rule and obtaining the virtual MCR of each of the connections and (b) guaranteeing the MCR of each of the connections using the virtual MCR of each of the connections.
According to the present invention, an MCR agreed between a user and a network at the time of the establishment of a connection is not used as a fixed value, but if there is an available rate band, a wider rate band can be used by each of active connections according to the use condition of the network resource by distributing the available rate band among the connections by a predetermined method. Thus, the rate band of a communication network can be more efficiently used, and simultaneously an available rate band can be impartially distributed among the connections, compared with a conventional method in which the management of an available rate band is not performed.